Fractional frequency generator



Feb. 8, 1949. BATCHELDER FRACTIONAL FREQUENCY GENERATOR Filed Dec. 27, 1945 INVENTOR. LAURENCE BATCHELDER I HIS ATTORzEY FlG.-2

Patented Feb. 8, 1949 2,460,800 FRACTIONAL FREQUENCY GENERATOR Laurence Batchelder, Cambridge,

Mass., assignor,

by mesne assignments, to Submarine Signal Company, Boston, Mass.,

ware

a corporation of Dela- Application December 27. 1945, Serial No. 637,415 12 Claims. (01. 250-36) The present invention relates to a frequency divider circuit for use in producing electrical oscillations of a fractional frequency of the input signal.

The basic method employed in producing fractional frequencies in electrical circuits is in the present instance related to regenerative modulation as early analyzed by the United States J. W. Horton Patent No. 1,690,299 and as further analyzed and described in an article by R. L. Miller of the Bell Telephone Laboratories in "Proceedings of the I. R. E.," volume 27, No. '7, pages 446 to 457.

The present invention is a modification and Improvement of the circuits described in these prior references. While in the Miller article the mathematical expressions set forth indicate that the phase angle between the input wave and the output wave is independent of the input amplitude and therefore independent of the output amplitude, which usually can be considered a part of the feed-back voltages, difiiculty has been experienced in maintaining oscillations in the circuit. In the circuit of the present invention this is overcome by a special arrangement of the varistor or rectifier in connection with the bridge circuit employed. The term varistor" is herein intended to mean any form of non-linear resistor or impedance element, whether rectifying or not, wherein the impedance or resistance is dependent on the value of the impressed voltage.

In the present invention the feed back is connected to a bridge circuit one branch of which contains the varistor across which the input signal is fed. When a voltage is applied, the resistance in the varistor is increased to such an extent as to unbalance the bridge and cause the grid'of the modulator to receive a positive feedback voltage. When no voltage is applied. the resistance of the varistor becomes small and the bridge balance is reversed so that the phase of the feed-back voltage is negative.

The basic theory of the operation of circuits of the type herein described does not attempt to determine the origin of the feed-back voltage. As in any regenerative oscillatory circuit the parameters of the circuit determine the frequency of oscillation which may, for example, be originally created by any transient or startin effect.

The present invention will be more fully un derstood in connection with the drawings annexed hereto illustrating an embodiment of the same in which Fig. 1 shows a divider circuit in cascade form in which a second fractional frequency is derived from the first; Fig. 2 shows a the frequency f1 in the 2 simplified diagram of a portion of the circuit of Fig. 1; and Fig. 3 shows a modification of the circuit in Fig. 2.

In the arrangement described in Fig. 2 the lines I deliver the output frequency f1 while the input frequency f: is impressed upon the input transformer 2 or fed to the lines 3, 4 in any usual manner. The output frequency ,fi in the simple case must fulfill the relationship that faif1=f1 or that Where no multiple or harmonic frequencies of feed-back circuit are created, the most general relationship which may exist is n mi 1) where both 1:. and, m are positive whole numbers or zero. See the article by Miller above referred to a non-linear element whose impedance between the terminals 6 and 1 is controlled and varied by the voltage of the input signal f2 impressed by transformer 2 across the terminals 3 and 4. This non-linear elementS makes the feed back degenerative with no signal and regenerative when a signal is impressed on the terminal leads 3 and 4. Under these conditions the circuit becomes self-oscillatory at a frequency 11 when an input signal is impressed upon it.

When no signal is impressed, the resistance between the points 6 and l is comparatively low and the potential of the point I connected to the modulating grid 8 through the resistor 9 approaches that of the point In connected to one side of the feed-back coil II which is coupled to a coil l2 in the circuit l3 tuned to the frequency f1 through the condenser H. In this condition the feed back is negative and the circuit is not oscillatory. When a voltage is impressed upon the lines 3 and 4, the resistances of the rectifiers connected to the point 1 are slightly lowered while the rethe input of 39 which is generally similar to that of the first terially increasing the resistance or impedance in the bridge varistor' element 5, thus driving the point 'I more nearly to the potential of the point l connected to the opposite end of the feed-back coil Ii from that to which the point I6 is connected. This in effect produces a positive feed back to sustain oscillation. Since the feed back is positive only during parts of each cycle of the input signal is, the frequency h of the oscillation is controlled by f: and is an exact fraction of f2.

The principle as explained in connection with Fig. 2 is applied also in the circuit ofFig. 1. The inp t frequency I: may be impressed across the terminals 26 through an initial amplifier circuit 2| and impressed upon the coupling transformer 22, the terminals of which are connected across the varistor bridge 23 in'the same manner as set forth in connection with Fig. 2. The feed-back coil 24 is connected across impedances 26 and 26 which form one side of the bridge, the other side ofwhich is formed by the varistor 23 and the impedance 21. the elements 26 and 26 as at 23 and the opposite side, namely at the point 26, is connected to the grid 36 through a resistance 3 I.

The elements of the bridge in Fig. 2 are correspondingly the same as in Fig. 1 with the impedances or resistances 32 and 33 corresponding to the resistances 26 and 25.

In the output of the vacuum tube 35, Fig. 1, which may be of the GAG? type, there is connected a tuned circuit 36 corresponding to the circuit l3 of Fig. 2 the coil of which is coupled both to the feed-back coil 24 and to the input coil 31 of the succeeding stage in which a vacuum tube 46 of the 6SL'7 type may be used. In the arrangement shown in Fig. 1 the output 'of the tube 46 from the frequency divider circuit 33 is impressed through coupling transformer 4| on the second frequency divider circuit frequency divider circuit 38.

If a 4 kc. signal is impressed upon the input at 26, a 2 kc. signal may be obtained from the output of the tube 46. and a 1 kc. signal will be obtainable at the final output terminal 42.

Voltages are supplied to the circuit of Fig. 1 through the rectifier 43 forming a part of the circuit of Fig. 1. In this rectifier alternating current may be supplied across the input terminals 44 and the usual B voltage may be obtained at the output between the ground 46 and the line 46.

Fig. 3 shows a simplification of Fig. 2 in which the elements are the same with the exception of the resistor or impedance 33 which is made adjustable for controlling the feed back balance.

The device of the present application finds various uses in electrical circuit and, as is shown in .Fig. 1, the device may be used in a cascade system for deriving a comparatively low frequency from a high frequency source.

Having now described my invention, I claim:

1. Means for obtaining a fractional frequency output in an electronic circuit comprising a vacuum tube oscillatory circuit having a tuned output circuit, an input circuit adapted to receive the signal of which a fractional frequency output is to be obtained, a feed back of the regenerative type connected between the tuned output and the input circuit including a bridge circuit having one branch only formed as a rectifier coupling said input circuit to the oscillatory circuit.

2. Means for obtaining a fractional frequency one branch The. bridge is grounded between output in an electronic circuit comprising a vacuum tube oscillatory circuit having a tuned output circuit, an input circuit adapted to receive the signal of which a fractional frequency output is to be obtained, a feed-back of the regenerative type connected between the tuned outputand the input circuit including a bridge circuit having formed as a rectifier coupling said input circuit to the oscillatory circuit, said rectifier forming itself a bridge circuit, the input circuit being connected diagonally across said rectifier bridge in diagonal relation to the connection of the rectifier bridge in the first-mentioned bridge circuit.

3. Means for obtaining a fractional frequency output in an electronic circuit comprising a vacuum tube oscillatory circuit having a tuned output circuit, an input circuit adapted to receive the signal of which a fractional frequency output is to be obtained, a feed back of the regenerative type connected between the tuned output and the input circuit including a bridge circuit having one branch formed as a rectifier coupling said input circuit to the oscillatory circuit, said rectifier having two branches connected in shunt across the input circuit providing current flows in opposite direction.

4. Means for obtaining a fractional frequency output in an electronic circuit comprising a vacuum tube oscillatory circuit having a tuned output circuit, an input circuit adapted to receive the signal of which a fractional frequency output is to be obtained, a feed back of the regenerative type connected between the tuned output and the input circuit including a bridge circuit having onebranch formed as a rectifier coupling said input circuit to the oscillatory circuit, said rectifier forming itself a bridge circuit, theinput circuit being connected diagonally across said rectifier bridge in diagonal relation to the connection of the rectifier bridge in the first-mentioned bridge circuit, the rectifier bridge circuit .providing current flow from one input terminal -to the other in opposite directions through different halves of the rectifier bridge.

5. Means for obtaining a fractional frequency output in an electronic circuit comprisinga vacuum tube oscillatory circuit having a tuned output circuit and an input circuit adapted to receive the signal of which a fractional frequency output is to be obtained, a feed back circuit including a bridge circuit one branch only of which contains a non-linear element whose impedance is dependent on the value of the received input signal.

6. Means for obtaining a fractional frequency output in an electronic circuit comprising a vacuum tube oscillatory circuit having a tuned output circuit and an input circuit adapted to receive the signal of which a fractional frequency output is to be obtained, a feed back circuit including a bridge circuit one branch only of which contains a non-linear element whose impedance is dependent on the value of the received input signal, said signal being applied to said'nonlinear bridge element.

-impedance' elements in three arms thereof, the

fourth arm containing a non-linear element whose impedance is dependent on the value of the applied voltage and adapted to receive thereacross a signal of which the frequency is to be converted; connections from one pair of opposite points of said bridge to the input of said oscillatory circuit; and means coupling the other pair of opposite points of said bridge to said output circuit for feeding back a portion of the output signal to said input circuit.

8. A frequency converter comprising: an oscillatory circuit having a tuned output circuit; an input circuit comprising a bridge having linear impedance elements in three arms thereof, the fourth arm containing a, non-linear element whose impedance is dependent on the value of the applied voltage and adapted to receive thereacross a signal of which the frequency is to be converted; connections from one pair of opposite points of said bridge to the input of said oscillatory circuit; and means coupling the other pair of opposite points of said bridge to said output circuit for feeding back a portion of the output signal to said input circuit; the arms of said bridge being dimensioned so that said bridge is unbalanced in a sense to provide positive feedback to said oscillatory circuit when the voltage of said signal exceeds a certain value.

9. A frequency converter comprising: an oscillatory circuit having a tuned output circuit;

an input circuit comprising a bridge having linear impedance elements in three arms thereof,

the fourth arm containing a non-linear element I whose impedance is dependent on the value of applied voltage and adapted to receive thereacross a signal of which the frequency is to be converted; said bridge arms being dimensioned so that said bridge is out of balance in one sense when the impressed signal has a desired operating value and in the opposite sense when said signal has a substantially lesser value; connections from one pair of opposite points of said bridge to the input of said oscillatory circuit. and means coupling the other pair of opposite points of said bridge to said output circuit for providing a positive feedback signal to said oscillatory circuit when said bridge is unbalanced in said one sense.

10. A frequency converter comprising: an oscillatory circuit having a tuned output circuit; an input circuit comprising a bridge having linear impedance elements in three arms thereof the fourth arm containing a second bridge comprising four non-linear elements poled in the same direction of which the impedance is dependent on the value of the applied voltage, connected in said am at one pair of opposite points and being adapted to receive a signal of which the frequency is to be converted at the other pair of opposite points, the four arms of the first named bridge being so proportioned that the bridge is out of balance in one sense when the impresseed signal has a desired operating value and in the opposite sense when said signal has a substantially lesser value; connections from one pair of opposite points of said first named bridge to the input of said oscillatory circuit; and means coupling the other pair of opposite points of said first named bridge to said output circuit for providing a positive feedback signal when said first named bridge is unbalanced in said one sense.

11. A frequency converter comprising: a vacuum tube oscillatory circuit having a tuned output circuit: an input circuit comprising a bridge having resistors in three arms thereof and in the fourth arm a non-linear element whose impedance is dependent on the value of applied voltage and adapted to receive thereacross the signal of which the frequency is to be converted; connections from one pair of opposite points of said bridge to the control grid and cathode respectively of the vacuum tube of said oscillatory circuit; and means connected across the other pair of opposite points of said bridge circuit for furnishing a portion of the energy of said tuned output circuit to said input circuit.

12. A frequency converter comprising: a vacuum tube oscillatory circuit having a tuned output circuit; an input circuit comprising a bridge having resistors in three arms thereof and in the fourth arm a non-linear element whose impedance is dependent on the value of applied voltage and adapted to receive thereacross the signal of which the frequency is to be converted; a connection from one end of said fourth arm to the control grid of the vacuum tube of said oscillatory circuit, and a connection from the opposite bridge point to the cathode of said tube; means for furnishing a portion of the energy of said tuned output circuit to said input circuit; and connections from said last mentioned means to the remaining pair of opposite points of said bridge. the side of said means that is oppositely phased to the control grid voltage being connected to the point at the other end of said fourth arm.

LAURENCE BATCHELDER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 3,159,59'7 Miller May 23, 1939 p 

